LIF and breast cancer: Breast cancer cell lines with low metastatic potential, defined by their lack of colonization of the lung or bone marrow following intravenous inoculation (e.g., MCF7, SUM159, and D2.0R cells), abundantly express LIFR and initiate downstream signals in response to recombinant LIF, but highly metastatic breast cancer cell lines (e.g., MDA-MB-231b, 4T1BM2, and D2A1 cells) do not express a functional LIFR and are unresponsive to recombinant LIF treatment [73], suggesting that the ability of cells to respond to LIF corresponds to their metastatic potential.